1. Field of the Invention
The present invention relates to a seatback frame structure that is installed in a his seatback of a seat.
2. Description of the Related Art
There have been proposed a variety of frame arrangements that are installed in the inside of a seatback of a seat. Such a seatback frame is provided in various configurations and structures meeting necessary structural stiffness properties and satisfying a demand of a person who sits on the seat. For example, some of such seatbacks are equipped with a plurality of wire springs stretched across a generally rectangular seatback frame which defines an external border of the seatback frame arrangement in order to provide the seatback with required stiffness, and some of such seatbacks are equipped with a wire net or a wire net-like plate that is supported by a plurality of springs mounted on a frame of the seatback frame arrangement so as to provide the seatback with required stiffness and elasticity. In recent years, there is a strong demand for various properties and qualities such as adaptability to automatic assembling and a light-weight seat, and a large space within a seatback for installing a side air bag unit therein if the seat is used as a vehicle seat. However, since the above mentioned seatback is typically too complicate in structure to satisfy the demand pointed above.
A seatback that seems to satisfy the above demand has been proposed in, for example, Japanese Unexamined Patent Publication No. 10-85079. The seatback disclosed in the publication has such a simple seatback frame structure that comprises transverse wires stretched across a seatback frame and vertical wires extending from the basal part of the seatback frame over the transverse wires so as to provide the seatback with stiffness. In this seatback frame structure, because the transverse wires, which elastically support the back of a person who sits on the seat, extend directly upward from the basal part of the seatback frame, all of the wires deform or deflect backward with respect to the bottom line of the seatback frame as a supporting point when the back of the person sitting on the seat leans on the seatback, so that the seatback can not provide lumbar support which refers to support of the back of the person in a fashion in conformity with the S-shaped backbone of the person. The seatback that is incapable of providing the lumbar support makes a person sitting on the seat hard to hold a sitting posture for a long period of time, which results in causing the person to feel pain.
It is an object of the present invention to provide a seatback frame structure for a seatback of a seat which has high adaptability to automatic assembling and a light-weight seat and provides a large space for a side air bag unit to be installed within a seatback if used for a vehicle seat.
It is another object of the present invention to provide a seatback frame structure for a seatback which provides lumbar support or support of the back of a person who sits on the seat in conformity with a shape of his or her backbone while is simple in structure.
According to one aspect of the present invention a seatback frame structure comprises a generally rectangular seatback frame which has opposite side frame sections extending vertically along opposite sides of a seatback, and a wire frame which has a pair of base frame sections extending substantially horizontally between and secured to lower parts of the opposite side frame sections, respectively, and an upward extending support frame section extending upward from the base frame sections and elastically deflectable backward with respect to the base frame sections. The wire frame may further comprise a downward extending support frame section disposed between each of the base frame sections and the upward extending support frame section and extending downward from the base frame section and elastically deflectable backward with respect to the base frame section.
The seatback frame structure thus configured causes backward elastic deflection at the upward extending support frame section and only a slight backward elastic deformation at the base sections when a person sits on the seat with his or her back leaning on the seatback with an effect of providing the person with a feeling of backward displacement at the upper part of the wire frame and firm lumbar support due to stiffness at the middle part of the wire frame. Accordingly, the seatback equipped with the seatback frame structure therein realizes support of the back of a person sitting on the seat in a fashion in conformity with the backbone of the person. The downward extending support frame section which is deflectable backward provides firm support of the back of a person siting on the seat nearly to a position corresponding to a coccyx of the person without giving the person a heterogeneous feeling and prevents the coccyx and buttocks of the person from changing backward in position on the seat, which gradually leads to a bad posture. Further, the wire frame increases stiffness of the seatback gradually in order of the upper part, the lower part and the middle part, so as to provide comfortable support of the back of the person sitting on the seat while the seatback frame structure is simple and at low costs.
According to another aspect of the present invention, a seatback frame structure comprises a generally rectangular seatback frame which has opposite side frame sections extending vertically along opposite sides of the seatback, and a wire frame which has a pair of base frame sections extending substantially horizontally between and secured to lower parts of the opposite side frame sections, respectively, at a height corresponding to a lumbar vertebra of a person who sits on the seat and an upward extending support frame section extending upward from the base frame sections to a height corresponding to shoulder blades of the person and elastically deflectable backward with respect to the base frame sections. The wire frame may further comprise a downward extending support frame section disposed between each of the base frame sections and the upward extending support frame section so as to extend downward to the height corresponding to the lumbar vertebras from the base frame sections and elastically deflectable backward with respect to the base frame sections.
The seatback frame structure thus configured provides more comfortable lumbar support in conformity with a body shape of a person siting on the seat due to the configuration of the wire frame that comprises the base frame sections extending transversely at a height of a lumbar position of the person and the upward extending support frame section extending to a position of shoulder blades of the person. Further, due to the downward extending support frame sections extending to the coccyx position of the person between the base frame sections and the upward extending support frame section, the seatback frame structure provides support of the back of the person along the backbone, which realizes back support of a person sitting on the seat in conformity with a body shape of the person. The horizontally extending base frame sections provides the wire frame at its basal part with high stiffness, so that the seatback is possible to have increased support rigidity at its middle part.
In these embodiments, the seatback frame structure may further comprise a deflection restricting member operative to restrict the wire frame to a specified backward deflection. Specifically, the deflection restricting member is disposed behind the upward extending support frame section of the wire frame and comprises a subsidiary wire frame extending between and secured to upper parts of the opposite side frame sections, respectively, so as to cross over the upward extending support frame section of the wire frame. Further, the deflection restricting member comprises an elastic member operative to suspend the upward extending support frame section from the generally rectangular seatback frame. The deflection restricting member limits the largest elastic deflection of the upward extending support frame section to a specified amount, so as to render the seatback to support the back of a person when the person sits deeply on the seat. The utilization of the subsidiary wire frame for the deflection restricting member ensures the seatback frame structure to be made simple in structure and to provide stable support of the back of the person sitting on the seat. The utilization of an elastic member for the deflection restricting member makes it possible to change backward deflection of the wire frame desirably by replacing the elastic member with other elastic members having different elasticity according to demands.
The seatback frame structure may further comprise elasticity exerting member operative to provide the wire frame with forward elasticity and to allow the upward extending support frame section to deflect only backward. The elasticity exerting member fixedly couples the wire frame at the upward extending support frame section to the generally rectangular seatback frame. The upward extending support frame section can be pre-urged forward by the elasticity exerting member, so that the seatback is provided with ensured support rigidity without increasing stiffness of the upward extending support frame section.
The wire frame may be configured so as to form a swelling between the upward extending support frame section and the downward extending support section, the swelling being directed forward at a height corresponding to a lumbar vertebra of a person who sits on the seat The swelling is directed forward from the front of the seatback and, in consequence, cooperates with the base frame sections to provide firm lumbar support even when the upward extending and the downward extending support frame section are deflected backward by the weight of the person sitting on the set.